1 00:00:01,000 --> 00:00:07,000 In an unprecedented 16-year-long study, using several of ESO’s flagship telescopes, 2 00:00:07,000 --> 00:00:11,000 astronomers have produced the most detailed view ever 3 00:00:11,000 --> 00:00:17,000 of the surroundings of the monster lurking at our Galaxy’s heart — a supermassive black hole. 4 00:00:17,000 --> 00:00:21,000 The research has unravelled the hidden secrets of this tumultuous region 5 00:00:21,000 --> 00:00:24,000 by mapping the orbits of almost 30 stars. 6 00:00:28,000 --> 00:00:30,000 This is the ESOcast! 7 00:00:30,000 --> 00:00:36,000 Cutting-edge science and life behind the scenes of ESO, the European Southern Observatory. 8 00:00:36,000 --> 00:00:43,000 Exploring the far reaches of the Universe with our host Dr J, a.k.a. Dr Joe Liske. 9 00:00:45,000 --> 00:00:48,000 Hello and welcome to the second episode of the ESOcast. 10 00:00:48,000 --> 00:00:51,000 Today, we have a very cool piece of science for you. 11 00:00:51,000 --> 00:00:55,000 A team of German astronomers, with characteristic precision and patience, 12 00:00:55,000 --> 00:01:02,000 has spent 16 years mapping out the motions of 28 stars orbiting the very centre of our Milky Way galaxy. 13 00:01:02,000 --> 00:01:04,000 Now, astronomers have believed for quite a while 14 00:01:04,000 --> 00:01:08,000 that the centre of our galaxy is the site of a supermassive black hole. 15 00:01:08,000 --> 00:01:11,000 Black holes are a consequence of General Relativity. 16 00:01:11,000 --> 00:01:19,000 They are objects that are so dense and whose gravity is so strong, that not even light can escape them. 17 00:01:19,000 --> 00:01:23,000 These observations that we are going to show you today are the best evidence yet 18 00:01:23,000 --> 00:01:28,000 that black holes are not just theoretical constructs, but actually do exist in reality. 19 00:01:28,000 --> 00:01:30,000 This is truly a milestone result. 20 00:01:31,000 --> 00:01:34,000 Observers under dark skies, far from the bright city lights, 21 00:01:34,000 --> 00:01:40,000 can marvel at the splendour of the Milky Way, arching in an imposing band across the sky. 22 00:01:40,000 --> 00:01:45,000 Zooming in towards the centre of our galaxy, about 25 000 light-years away, 23 00:01:45,000 --> 00:01:49,000 you can see that it is composed of myriads of stars. 24 00:01:49,000 --> 00:01:55,000 This is a pretty impressive sight, but much is hidden from view by interstellar dust, 25 00:01:55,000 --> 00:02:00,000 and astronomers need to look using a different wavelength, the infrared, that can penetrate the dust clouds. 26 00:02:00,000 --> 00:02:05,000 With large telescopes, astronomers can then see in detail the swarm of stars 27 00:02:05,000 --> 00:02:11,000 circling the supermassive black hole in the same way that the Earth orbits the Sun. 28 00:02:12,000 --> 00:02:16,000 The Galactic Centre harbours the closest supermassive black hole known, 29 00:02:16,000 --> 00:02:21,000 and the one that is also the largest in terms of its angular diameter on the sky, 30 00:02:21,000 --> 00:02:26,000 making it the best choice for a detailed study of black holes. 31 00:02:27,000 --> 00:02:30,000 So what this team did was that, at various points over the past 16 years, 32 00:02:30,000 --> 00:02:34,000 they kept taking images of the very central region of the Milky Way. 33 00:02:34,000 --> 00:02:39,000 Now, from these images, they were able to map out the motions of a total of 28 stars. 34 00:02:40,000 --> 00:02:44,000 Now, what these motions showed was that these stars aren’t just moving about randomly, 35 00:02:44,000 --> 00:02:48,000 but that they are clearly orbiting a very massive, central object. 36 00:02:48,000 --> 00:02:52,000 And the point is that this central object is completely unseen. 37 00:02:52,000 --> 00:02:56,000 Now, from the motions it’s also possible to deduce the mass of the central object. 38 00:02:56,000 --> 00:03:01,000 It came out to be a little over four million times the mass of the Sun. 39 00:03:01,000 --> 00:03:03,000 Now, what’s more, 40 00:03:03,000 --> 00:03:06,000 that enormous mass has to fit into a tiny little volume, 41 00:03:06,000 --> 00:03:11,000 and so one cannot escape the conclusion that the central object really is a black hole. 42 00:03:12,000 --> 00:03:17,000 The observing campaign started with observations made in 1992 43 00:03:17,000 --> 00:03:23,000 with the SHARP camera attached to ESO’s 3.5-metre New Technology Telescope (NTT), 44 00:03:23,000 --> 00:03:26,000 housed at the La Silla observatory in Chile. 45 00:03:27,000 --> 00:03:30,000 More observations have subsequently been made in the last few years 46 00:03:30,000 --> 00:03:38,000 using two instruments mounted on ESO’s 8.2-metre Very Large Telescope (VLT). 47 00:03:38,000 --> 00:03:45,000 Over the 16 years of this study, ESO’s telescopes have stared at this one region for 50 full nights. 48 00:03:46,000 --> 00:03:48,000 This new research marks the first time 49 00:03:48,000 --> 00:03:52,000 that so many of these central stars have had their orbits determined so precisely. 50 00:03:53,000 --> 00:03:57,000 The data also reveal a lot about the characteristics of these stars and how they must have formed. 51 00:03:58,000 --> 00:04:03,000 For one of the stars, the astronomers were even able to follow it for a complete orbit! 52 00:04:03,000 --> 00:04:07,000 The star approached the central black hole to within just one light-day. 53 00:04:07,000 --> 00:04:10,000 That’s just five times the distance between Neptune and the Sun. 54 00:04:11,000 --> 00:04:15,000 Professor Reinhard Genzel, from the Max Planck Institute for Extraterrestrial Physics in Germany, 55 00:04:15,000 --> 00:04:18,000 is the leader of the team that made the discovery. 56 00:04:18,000 --> 00:04:21,000 Reinhard, why is it so important to study the centre of the Milky Way? 57 00:04:22,000 --> 00:04:26,000 Well, you see, the Milky Way centre is one of the most important laboratories we have 58 00:04:26,000 --> 00:04:31,000 to study in very great detail what’s happening in the centres of galaxies, 59 00:04:31,000 --> 00:04:35,000 in much more detail than we can ever hope to do in all other galaxies. 60 00:04:35,000 --> 00:04:40,000 Yet, here we are, we can study whether there is a central black hole, what happens around it and so forth, 61 00:04:40,000 --> 00:04:43,000 all very general issues which we would like to explore 62 00:04:43,000 --> 00:04:48,000 and which you cannot really study that much in detail in other galactic nuclei. 63 00:04:49,000 --> 00:04:53,000 Dr Stefan Gillessen is the first author of the paper reporting this study. 64 00:04:54,000 --> 00:04:57,000 So Stefan, tell us, what’s the most important result you obtained? 65 00:04:57,000 --> 00:05:00,000 The most important result of our research really is 66 00:05:00,000 --> 00:05:06,000 that we have now empirical evidence for the existence of a massive black hole in the centre of our Milky Way. 67 00:05:06,000 --> 00:05:10,000 The mass of this black hole is around four million solar masses 68 00:05:10,000 --> 00:05:13,000 and we know the mass at the percent level. 69 00:05:13,000 --> 00:05:17,000 This is of course an amazing result, but the team doesn’t plan to stop here. 70 00:05:18,000 --> 00:05:21,000 Now, in the past they’ve used the novel technique of adaptive optics 71 00:05:21,000 --> 00:05:23,000 to remove the blurring effects of the atmosphere. 72 00:05:23,000 --> 00:05:26,000 In the future, they plan to do even better, 73 00:05:26,000 --> 00:05:31,000 and to get even higher resolution images by using another new technique called interferometry. 74 00:05:31,000 --> 00:05:36,000 This is where you combine the light from two or more of the VLT’s Unit Telescopes together. 75 00:05:37,000 --> 00:05:39,000 So Reinhard, what’s the next step? 76 00:05:39,000 --> 00:05:43,000 Well, you see, at this point, we really are fairly sure 77 00:05:43,000 --> 00:05:46,000 that there is a massive black hole at the centre of our Milky Way. 78 00:05:46,000 --> 00:05:48,000 The next thing, we want to actually play with it! 79 00:05:48,000 --> 00:05:52,000 Play with it in the sense that we want to use it as a tool 80 00:05:52,000 --> 00:05:57,000 to test whether General Relativity, the theory of Einstein, is actually wrong or right. 81 00:05:58,000 --> 00:06:01,000 Wow! Playing with a black hole to test relativity... 82 00:06:01,000 --> 00:06:03,000 That’s pretty cool stuff! 83 00:06:03,000 --> 00:06:06,000 I’m Dr J signing off for the ESOcast. 84 00:06:06,000 --> 00:06:09,000 Join me again next time for another cosmic adventure. 85 00:06:11,000 --> 00:06:14,000 ESOcast is produced by ESO, the European Southern Observatory. www.eso.org 86 00:06:14,000 --> 00:06:17,000 ESO, the European Southern Observatory, is the pre-eminent intergovernmental science and technology organisation in astronomy 87 00:06:17,000 --> 00:06:20,000 designing, constructing and operating the world's most advanced ground-based telescopes. 88 00:06:21,000 --> 00:06:23,000 Transcription by ESO ; translation by —